Sphygmomanometer

ABSTRACT

The objective of the present invention is to provide a sphygmomanometer that is easy to use. The sphygmomanometer according to the present invention measures blood pressure in accordance with an oscillation in an artery wall, resulting from an arterial pulse correspondent with a change in cuff pressure. It comprises a cuff that is connected to the sphygmomanometer main body by a tube, a display unit for displaying the results of blood pressure measurements, and an air supply unit for supplying air to, and thus pressurizing, the cuff, which is detachable from the sphygmomanometer main body. The air supply unit is screwed into the sphygmomanometer main body with a screw assembly, and the screwed-in state is preserved by a caulking ring. The air supply unit also comprises a filter for keeping dust from entering the sphygmomanometer main body.

This application is a divisional of U.S. application Ser. No. 11/662,207filed on Mar. 18, 2008 which is a U.S. national stage application basedon International Application No. PCT/JP2005/016768 filed on Sep. 12,2005 and which claims priority under 35 U.S.C. §119 to JapaneseApplication No. 2004-264562 filed on Sep. 10, 2004, the entire contentof all three of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a sphygmomanometer that is used in a hospitalor other facility, by a nurse or other medical professional, to measurea patient's blood pressure, and, in particular, that is portable andallows selecting from a plurality of types of cuffs.

BACKGROUND DISCUSSION

A sphygmomanometer that sends air from an air supply sphere, i.e., arubber bulb, to a cuff, via the sphygmomanometer main body, is disclosedin, for example, Japanese Patent Publication Laid Open 61-79440 andJapanese Patent Publication Laid Open 2004-81743.

FIG. 1 depicts a sphygmomanometer comprising a Korotkov sound sensor asdisclosed in the cited reference 1. In the sphygmomanometer depicted inFIG. 1, a sphygmomanometer main body 1301 and a cuff 1302 are joined bya rubber tube 1304 and a lead line 1305. A rubber bulb that supplies air1303 is also connected to the cuff 1302.

FIG. 2 depicts a sphygmomanometer as disclosed in the cited reference 2.The sphygmomanometer comprises a flexible first air tube 1405 and asecond air tube 1406 that communicate with either a sphygmomanometermain body 1401 and a cuff 1404, or the sphygmomanometer 1401 and theopen atmosphere, with the tubes less likely to interfere with a displayunit 1402 or a control unit 1403, owing to the relation between thefirst air tube 1405 and the second air tube 1406 being configured asdepicted in FIG. 2, thus making the display easier to see, and the powerswitch and other aspects of the control unit 1403 easier to operate.

The sphygmomanometers disclosed in the cited reference 1 and 2, however,have the air supply sphere connected, via the air tube, either to thecuff or to the sphygmomanometer main body, and thus, thesphygmomanometer main body must be maintained with one hand, and the airsupply sphere held, and pressure applied, with the other hand, resultingin poor usability.

Another problem is that connecting the respective units by tubes, as perthe sphygmomanometers disclosed in the cited references 1 and 2,increases the overall size of the sphygmomanometer.

SUMMARY

The present invention, devised with the foregoing problems in mind, hasas its objective the provision of a smaller, portable, easy to usesphygmomanometer.

In order to achieve the objective, the sphygmomanometer according to thepresent invention measures blood pressure based on a fluctuation in anartery wall resulting from an arterial pulse in accordance with a changein cuff pressure. It comprises a cuff that is connected to asphygmomanometer main body by a tube, a display unit for displayingresults of measuring blood pressure, and an air supply sphere fordelivering air to, and pressurizing, the cuff, wherein the air supplysphere is detachable from the sphygmomanometer main body, constituting aportion of the sphygmomanometer main body when attached to thesphygmomanometer main body.

The air supply sphere comprises a connector unit for connecting the airsupply sphere to the sphygmomanometer main body, and a filter within theconnector unit for preventing dust from entering the sphygmomanometermain body.

The connector unit is screwed into the sphygmomanometer main body by ascrewing assembly, and is maintained in the screwed-in state by a ringof caulk.

A sphygmomanometer in which an o-ring is fitted into the screwingassembly of the air supply sphere, such that the air supply sphere willbe disengaged from the sphygmomanometer main body only with difficulty.

An o-ring is fitted into the screwing assembly of the air supply sphere,such that the air supply sphere will be disengaged from thesphygmomanometer main body only with difficulty.

It is permissible to fit a ring, other than an o-ring, that possesses aone-way clutch assembly, to the air supply sphere's screwing assembly,and a protrusion is formed wherein the one-way clutch assembly fits.

The cuff is selected from among a plurality of types of cuffs ofdifferent sizes.

The cuff comprises a large cuff, to stop blood flow, and a small cuff,for detecting a pulse. A unit of the large cuff that connects the largecuff to the tube is made with a protrusion that has a tapering portion.A unit of the small cuff that connects the small cuff to the tube ismade to connect to the small cuff by being slackened and twistedvis-à-vis the large cuff tube, the outer diameter of which is largerthan that of the small cuff tube.

Other characteristics of the present invention will be apparent from thedisclosures of the preferred embodiments and the attached drawings, asgiven hereinafter.

According to the sphygmomanometer of the previous invention, the tubefor connecting the air supply sphere to the sphygmomanometer main bodyis eliminated, making the two components into a single unit, allowingone-handed air supply and pressurization, tremendously improving ease ofuse, and allowing miniaturization of the overall size of thesphygmomanometer.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Other characteristics and advantages of the present invention will beapparent from the following descriptions, with reference to the attacheddrawings. Portions of the attached drawings that are identical orsubstantially similar to one another will be designated with identicalreference numbers.

The attached drawings are included with the specification and constitutea portion thereof. They are used to depict the embodiment of theinvention, and to describe the principles of the invention, togetherwith the descriptions thereof.

FIG. 1 depicts a first concrete example of a conventionalsphygmomanometer.

FIG. 2 depicts a second concrete example of a conventionalsphygmomanometer.

FIG. 3 depicts an external view of a sphygmomanometer according to theembodiment.

FIG. 4A and FIG. 4B depict an assembly of a cuff 2 according to theembodiment.

FIG. 5 depicts an internal assembly of a sphygmomanometer main bodyaccording to the embodiment.

FIG. 6 depicts a connector for connecting a sphygmomanometer main bodyto a cuff tube.

FIG. 7 depicts a portion of the sphygmomanometer main body that housesthe connector in FIG. 6.

FIG. 8 depicts an external view of a portion that connects asphygmomanometer and a cuff tube.

FIG. 9 depicts a connection of a cuff tube, i.e., a small cuff tube, tothe sphygmomanometer main body.

FIGS. 10A, 10B, and 10C depict an assembly of a connection unit betweenan air supply sphere 15 and the sphygmomanometer main body.

FIGS. 11A, 11B, and 11C depict an assembly of a connection unit betweenan air supply sphere 15 and the sphygmomanometer main body 10, accordingto a different concrete example of a connector.

FIGS. 12A, 12B, and 12C depict an assembly of a one-way clutch ring on aconnection unit between an air supply sphere 15 and the sphygmomanometermain body 10, pertaining to a connection unit between an air supplysphere 15 and the sphygmomanometer main body 10.

FIG. 13 depicts a concrete example of a sphygmomanometer display unit.

FIG. 14 depicts a circuit block diagram of a sphygmomanometer main body.

FIG. 15 is a graph depicting a pressure change when pressure declines.

FIG. 16 is a graph depicting an estimated measured value and an actualmeasured value of a pressure change when pressure declines.

FIG. 17 is flowchart describing an operation that determines systolicand diastolic pressure.

FIG. 18 depicts an assembly of an electromagnetic valve 38 that is usedin a sphygmomanometer.

FIG. 19 is a hysteresis property that depicts a relationship between anapplied voltage and a switching stroke as pertains to an opening of theelectromagnetic valve 38 under normal circumstances.

FIG. 20 depicts a circumstance wherein a tilt has occurred within arubber valve 381 of the electromagnetic valve 38.

FIG. 21 is a hysteresis property that depicts a relationship between anapplied voltage and a switching stroke as pertains to an opening of theelectromagnetic valve 38 when the electromagnetic valve 38 is tilted.

FIG. 22 depicts a suggested modification to an electromagnetic valve.

FIGS. 23A and 23B are graphs depicting a pressure change when pressureincreases.

DETAILED DESCRIPTION

Following is a detailed description of the embodiments of the invention,with reference to the attached drawings.

<Sphygmomanometer External View>

FIG. 3 depicts an external view of a sphygmomanometer 1 and a cuff 2according to the embodiment.

In FIG. 3, No. 10 is a casing of a sphygmomanometer main body, withinwhich are contained a substrate, upon which is carried an electricalcircuit for electrically operating the sphygmomanometer 1, and a tube,described hereinafter, for sending air to, and exhausting air from, acuff 2, the latter of which in turn comprises a large cuff 22, that is,a large-capacity air bag, and a small cuff 23, that is, a small-capacityair bag, which are both described hereinafter. No. 11 is a display unit,wherein are displayed such elements as a systolic and a diastolic bloodpressure value, a pulse rate, and a measurement mode. No. 12 is anOn/Off Power Switch, and No. 13 is a mode switch. Regarding a mode ofthe sphygmomanometer 1 according to the embodiment, which will bedescribed hereinafter, there are a plurality of measurement modes, threein the present instance, that are built into the sphygmomanometer 1,being a normal mode, a slow mode, and a stethoscope mode. No. 14 is anexhaust switch, and pressing thereupon allows air in the large cuff 22to be forcibly exhausted. No. 15 is an air supply sphere, i.e., a rubberbulb, which supplies air to the cuff 2 via the tube within the casing 10by repeated squeezing and releasing.

The air from the air supply sphere 15 is sent to the cuff 2 via a tube18 and a tube 19 that are connected to a connector unit 16. No. 18 is atube for sending air to the large cuff 22, i.e., a large cuff tube, andNo. 19 is a tube for sending air to the small cuff 23, i.e., a smallcuff tube.

No. 17 is a tube holder, for preventing the large cuff tube 18 and thesmall cuff tube 19, which are a single unit from the point of the tubeholder 17 on toward the cuff 2, from separating from one another. Bymaking the small cuff tube 19 flexible, i.e., keeping it from beingstrained, between the connector unit 16 and the tube holder 17 makes itdifficult for the small cuff tube 19 from being disconnected from theconnector unit 16. It is possible to avoid the small cuff tube 19 comingapart from the connector unit 16, even if the tube is tugged on, or ifthe tube is pulled in a direction that it most likely was not meant togo, such that the large cuff tube 18 will not come loose, to the extentthat strain is kept off the small cuff tube 19.

The cuff 2 is covered with a cuff cover 21, within which is the largecuff 22, which is formed of a flexible material, which may include, butis not limited to, natural rubber, synthetic rubber, or an elastomer,and the small cuff 23, which is formed of a flexible material, which mayinclude, but is not limited to, polyurethane.

FIG. 4A and FIG. 4B depict an assembly of the cuff 2. FIG. 4A depictswhole structure, and FIG. 4B depicts a structure of the large cuff 22and the small cuff 23. As depicted in FIG. 4A, the cuff 2 comprises thecuff cover 21, in which is a surface fastener on an outer surface (notshown), and the large cuff 22 and the small cuff 23, which are coveredby the cuff cover 21. It is possible to, for example, replace ordisinfect the cuff 2, and a protrusion portion 22 a, with a taper unit22 b, is made a part of the large cuff 22, in order that the large cuff22 and the small cuff 23 may be easily inserted into, and removed from,an opening 2 a. When the protrusion portion 22 a is inserted into thecuff 2, the protrusion portion 22 a corresponds to the position of theopening 2 a. The protrusion portion 22 a is placed in a positionoff-center in the lengthwise direction of the cuff 22, i.e., L4 isgreater than L5, to avoid being inserted backwards.

The large cuff 22 is pressurized by air supplied thereto via the largecuff tube 18. By being pressurized and inflated, the large cuff 22 cutsoff blood flow to an arm, around which the cuff 2 is wrapped, of aperson whose blood pressure is being measured. The small cuff 23 is alsopressurized by air supplied thereto, via the small cuff tube 19. Whenair pressure in the large cuff 22 is reduced by exhaust, and blood flowis restored, a fluctuation occurs in the pressure of the air in thesmall cuff 23, and a pulse wave that corresponds to the fluctuation isdetected by a pressure sensor 92 (see FIG. 14 for details). A backingsheet made of PET (not shown) is placed between the large cuff 22 andthe small cuff 23, which is engineered so as to facilitate detection ofa slight pressure fluctuation within the small cuff 23. Given that thelarge cuff 22 possesses elasticity in its inflated state, placing thesmall cuff 23 directly next to the large cuff 22 would have a potentialfor failing to detect the pressure fluctuation within the small cuff 23,even if the fluctuation should be present. To avoid such a circumstance,the small cuff tube 19 is slackened and twisted vis-à-vis the large cufftube 18, which has an outer diameter that is wider than that of thesmall cuff tube 19, as the small cuff tube 19 is connected to the smallcuff 23. The small cuff tube 19 is twisted once according to theembodiment, although a plurality of twisting is permissible. Theassembly has the effect of avoiding the small cuff tube 19 separatingwhen being inserted into, and detached from, the cuff 2. Absorption byslackening and twisting has the effect of avoiding the small cuff tube19 being snagged when being inserted into, and detached from, the cuff2.

It is also possible for a nurse to use the surface fastener to securelyattach the cuff 2 to an upper arm of a patient, i.e., an examinee. It isnot necessary to detach a ring (not shown) to do so. The surfacefastener is built in because it becomes more difficult to wrap andsecure the cuff 2 as it gets larger.

No. 24 is a tube connector which is connected to the connector unit 16on the sphygmomanometer main body. No. 25 is a forcible exhaust valvewhich is built in with a large cuff size, i.e., L or XL. Cuff size willbe described hereinafter. With a large cuff size, the large cuff 22becomes larger out of necessity, and time is required to deflate from asufficiently inflated state, and it is possible to discharge the air ofthe large cuff 22 in a short amount of time by opening the forcibleexhaust valve 25, when one wants to let the air out of the large cuff 22rapidly.

A plurality of sizes of cuffs are provided according to the embodiment.In increasing order of size, the sizes are XS, S, M, L, and XL.

With regard to the XS size cuff, for example, a length L1 and a width W1of the cuff cover 21 is 345 mm plus or minus 5 mm and 100 mm plus orminus 4 mm, a length L2 and a width W2 of the large cuff 22 is 130 mmplus or minus 10 mm and 80 mm plus or minus 5 mm, and a length L3 and awidth W3 of the small cuff 23 is 30 mm plus or minus 1 mm and 20 mm plusor minus 1 mm.

With regard to the S size cuff, for example, a length L1 and a width W1of the cuff cover 21 is 435 mm plus or minus 5 mm and 130 mm plus orminus 4 mm, a length L2 and a width W2 of the large cuff 22 is 170 mmplus or minus 10 mm and 110 mm plus or minus 5 mm, and a length L3 and awidth W3 of the small cuff 23 is 40 mm plus or minus 1 mm and 25 mm plusor minus 1 mm.

With regard to the M size cuff, for example, a length L1 and a width W1of the cuff cover 21 is 520 mm plus or minus 5 mm and 150 mm plus orminus 4 mm, a length L2 and a width W2 of the large cuff 22 is 240 mmplus or minus 10 mm and 130 mm plus or minus 5 mm, and a length L3 and awidth W3 of the small cuff 23 is 60 mm plus or minus 1 mm and 30 mm plusor minus 1 mm.

With regard to the L size cuff, for example, a length L1 and a width W1of the cuff cover 21 is 640 mm plus or minus 5 mm and 190 mm plus orminus 4 mm, a length L2 and a width W2 of the large cuff 22 is 320 mmplus or minus 10 mm and 170 mm plus or minus 5 mm, and a length L3 and awidth W3 of the small cuff 23 is 80 mm plus or minus 1 mm and 40 mm plusor minus 1 mm.

With regard to the XL size cuff, for example, a length L1 and a width W1of the cuff cover 21 is 220 mm plus or minus 4 mm and 830 mm plus orminus 5 mm, a length L2 and a width W2 of the large cuff 22 is 420 mmplus or minus 10 mm and 200 mm plus or minus 5 mm, and a length L3 and awidth W3 of the small cuff 23 is 100 mm plus or minus 1 mm and 50 mmplus or minus 1 mm.

FIG. 5 depicts an internal assembly of a sphygmomanometer main body 10.

In FIG. 5, No. 31 is a manifold, No. 32 is a manifold junction unit, No.33 is a large cuff conduit, No. 34 is a bypass tube, i.e., a small cuffconduit, No. 35 is a conduit junction unit, No. 36 is a pressure sensorconduit, No. 37 is a bend prevention coil, No. 38 is an electromagneticvalve, and No. 39 is a caulking ring. No. 161 is a large cuff maleconnector for connecting the large cuff conduit 33 to the large cufftube 18, and No. 162 is a small cuff female connector for connecting thesmall cuff conduit 34 to the small cuff tube 19. The large cuff maleconnector 161 and the small cuff female connector 162 are formed as asingle unit, and form the connector unit 16.

Air supplied from the air supply sphere 15 passes through the manifold31 and is discharged from the large cuff male connector 161, via thelarge cuff conduit 33. Air discharged from the large cuff male connector161 is sent to the large cuff 22, passing through the large cuff tube18. Thus is the large cuff 22 pressurized.

A portion of the air supplied from the air supply sphere 15 enters thebypass tube 34 from the manifold junction unit 32, and, passing throughthe bypass tube 34, is discharged from the small cuff female connector162. Air discharged from the small cuff female connector 162 is sent tothe small cuff 23, passing through the small cuff tube 19. Thus is thesmall cuff 23 pressurized.

The pressure sensor conduit 36, which branches off from the conduitjunction unit 35, is in place to both send the portion of air that isrouted from the bypass tube 34 to a pressure sensor, i.e., No. 92 in theblock diagram in FIG. 14, and also to send the air that is forced out bythe pressure of the small cuff 23 that fluctuates with the pressure waveduring measurement to the pressure sensor. The bend prevention coil,i.e., a bend prevention unit material, 37 is within the pressure sensorconduit 36, which possesses a function of avoiding the tube beingblocked by a breakage of the pressure sensor conduit 36 when thepressure sensor conduit 36 is bent.

The bypass tube 34 is made, for example, from an olefin type ofelastomer, has an internal diameter on the order of 0.4 mm, with anarrow-gauge pipe similarly 0.4 mm in diameter, with stainless steel orother metallic property at either end, reinforcing the connectors ateither end such that they do not collapse, allowing maintenance of theinner diameter. The electromagnetic valve 38 is controlled to closewhile air is being sent via the air supply sphere 15, causing sufficientair to be sent to the cuff 2, and to open when exhausting air from, anddepressurizing, the large cuff 22. While air is also exhausted from thesmall cuff 23, the quantity is very small compared with that of thelarge cuff 22. The open and close control and other aspects of theelectromagnetic valve 38 are described hereinafter.

FIGS. 6 through 8 are detailed depictions of a component that connectsthe cuff tubes 18 and 19 to the sphygmomanometer main body 1. FIG. 6depicts the connector unit 16, FIG. 7 depicts an assembly of a connectorunit within the sphygmomanometer main body 1, and FIG. 8 depicts a planview of the component that connects to the cuff tube, when the componentis housed within the sphygmomanometer main body 1. FIG. 9 is an enlargedview of the large cuff tube connector 24.

In FIG. 6, No. 161 is a large cuff male connector, and No. 162 is asmall cuff female connector. No. 163 is a small cuff conduit connectorunit, No. 164 is a pressure sensor conduit connector unit, and No. 165is a large cuff conduit connector unit. No. 166 is a baseplate unit,which make the large cuff male connector 161 and the small cuff femaleconnector 162 into a single unit. No. 167 is an o-ring fitted into thedepression of the small cuff female connector 162.

In FIG. 7, No. 71 is a housing unit for the small cuff female connector162, No. 72 is a housing unit for the baseplate unit 166 that is withinthe small cuff female connector, and No. 73 is a housing unit for thebaseplate unit 166 that is within the large cuff male connector. Adepression, or fastening, 74 in the connector unit within thesphygmomanometer main body is built in to fasten the tube connector 24.A protrusion 75 is also built therein, because the depression 74 isbuilt therein.

The baseplate unit 166 of the connector unit 16 is housed within thehousing unit 72 and 73 in FIG. 7, with a position determined such thatthe connector unit 16 neither shifts, nor becomes unsteady, within thesphygmomanometer main body 1. The cylindrical small cuff femaleconnector 162 is housed within the small cuff female connector housingunit 71. Building a housing unit that is fitted to the shape of theconnector unit 16 within the casing of the sphygmomanometer main body 1allows avoiding unsteadiness on the part of the connector unit 16, aswell as performance of connecting the cuff tube to the sphygmomanometermain body 1 in a stable fashion.

As depicted in FIG. 8, the connection unit of the sphygmomanometer mainbody 1 is formed by fitting the upper casing and the lower casingthereof. The tip portion of the large cuff male connector 161 protrudesfrom the sphygmomanometer main body 1 to an extent; refer to FIG. 9 fora view of the protrusion. The protrusion 75 forms a flange thatsurrounds the perimeter of the component wherein the tube connector 24is connected to the small cuff female connector 162.

As depicted in FIG. 9, the tube connector 24 comprises a tip unit 241,for communicating air pressure that changes within the small cuff 23 tothe sphygmomanometer main body, an elastic unit 242, for securing thetube connector 24 itself within the connection unit of thesphygmomanometer main body, and a protrusion 243, which is formed on thetip of the elastic unit 242, which in turn is constituted of a pluralityof elements that are cut in the circumference of a portion of anexternal wall unit 244, which is formed so as to encompass the tip unit241. When the tube connector 24 is connected to the small cuff femaleconnector 162, the blade spring 243 fits into the depression 74, and theprotrusion 243 and the protrusion 75 on the sphygmomanometer main bodygrip the tube connector 24, which makes it difficult for the tubeconnector 24 to come apart from the sphygmomanometer main body.

The interior of the small cuff female connector 162 contains the o-ring167, which eliminates a gap that may emerge between the tip unit 241 andthe small cuff female connector 162, thus avoiding air leakingtherefrom.

When the protrusion 243 of the tube connector 24 is fitted into thedepression 74 of the sphygmomanometer main body 1, the gauge that isregulated with the blade spring protrusion 243 is larger than the gaugethat is regulated with the protrusion 75 of the sphygmomanometer mainbody, giving rise to a clicking sensation, owing to the resiliency ofthe elastic unit 242. The clicking sensation allows the user to easilydetermine that the tube connector 24 is connected to thesphygmomanometer main body 1.

FIGS. 10A through 10C depict an assembly of a connection unit between anair supply sphere 15 and a sphygmomanometer main body casing 10. FIG.10A depicts the air supply sphere 15 as fitted into the casing 10, FIG.10B depicts the air supply sphere 15 when detached from the casing 10,and FIG. 10C is a cutaway enlargement of an air supply sphere connector.

In FIG. 10A, No. 101 is the air supply sphere connector, Nos. 102 a and102 b are o-rings, No. 103 is a mesh dust filter, and No. 104 is afilter cap. A small diameter o-ring 102 a has a sealing effect in acircumference direction, and a large diameter o-ring 102 b has an effectof preventing slack by being compressed, or deformed, in an axialdirection. Placing the two o-rings 102 a and 102 b provides the twoeffects.

As depicted in FIG. 10B, the air supply sphere connector 101 is fittedwith a screw thread 1014, and fitting of the air supply sphere 15 isperformed by screwing the air supply sphere connector 101 into themanifold 31.

The air supply sphere connector 101 is inserted into the air supplysphere 15 from an insertion unit 1010 to a flange unit 1012. The airsupply sphere connector 101 is fitted with an expanded diameter stepunit 1011, which provides resistance near the insertion point of therubber air supply sphere 15, which makes it difficult for the air supplysphere 15 to come undone from the connector. The caulking ring 39,according to FIG. 10A, constricts near the insertion point of the rubberair supply sphere 15 from outside, making it even more difficult for theair supply sphere 15 to come undone from the air supply sphere connector101. The expanded diameter step unit 1011 and the caulking ring 39 ofthe air supply sphere connector 101 secure the air supply sphere 15 andthe air supply sphere connector 101 from within and without.

The peripheral outside of the air supply sphere connector 101 is formedof a depression 1013. As depicted in FIG. 10A, for example, the rubbero-rings 102 a and 102 b are fitted, forming a seal when the air supplysphere 15 is screwed into the manifold 31. The o-ring 102 b serves toprevent slack when the air supply sphere 15 is screwed into the manifold31.

The air supply sphere connector 101 possesses a filter mounting unit1015, within which is mounted a filter cap 104, which is fitted onto thedust filter 103, which, in turn, is capable of preventing dust gettinginto components within the sphygmomanometer 1 that may include, but arenot limited to, the conduits 33, 34, and 36, the electromagnetic valve38, and the tubes 18 and 19 that lead to the cuff 2. It is thus possibleto prevent the tubes being blocked, or a malfunction in theelectromagnetic valve 38 or the pressure sensor 92. No. 1020 is a checkvalve.

FIGS. 11A, 11B, and 11C and FIGS. 12A, 12B, and 12C depict a secondconcrete example of an assembly of a connection unit between the airsupply sphere 15 and the sphygmomanometer main body casing 10. Inparticular, FIGS. 11A, 11B, and 11C depict a second concrete example ofan assembly of the air supply sphere connector 101, and FIGS. 12A, 12B,and 12C depict a second concrete example of an assembly of a one-wayclutch ring 1201.

Whereas in the first concrete example, the o-ring 102 b was fitted intothe depression 1013 of the air supply sphere connector 101, the one-wayclutch ring 1201 is fitted in place of the o-ring 102 b in the secondconcrete example, as per FIGS. 12A and 12B.

As depicted in FIGS. 12A and 12B, the underside of the one-way clutchring 1201 has, for example, 12 trapezoidal cutout units 1202, spaced atregular intervals. As depicted in the enlargement in FIG. 12C, thecutout units 1202, the angle of one end of a portion, signified by the“Y” in the diagram, is an outline right angle, whereas the other end hasa slant, the angle of which forms a prescribed angle θ, between 15 and30 degrees, for example. An elastic ring 1203, for example, a foamrubber ring, a sponge ring, a rubber ring, or the like, is adhered tothe upper side of the one-way clutch ring 1202. The effect of theelastic ring 1203 is described hereinafter.

As depicted in FIG. 11A, the flange unit 1012 of the air supply sphereconnector 101 has, for example, four trapezoidal protrusion units 1102,spaced at regular intervals. As depicted in the enlargement in theportion marked X in FIG. 11B, the angle of one end of a portion is anoutline right angle, whereas the other end has a slant, the angle ofwhich forms a prescribed angle θ, between 15 and 30 degrees, or in otherwords, the same angles as the angles of the cutout units 1202.Accordingly, the relationship between the trapezoidal protrusion units1102 and the trapezoidal cutout units 1202 is such that they fittogether precisely.

The one-way clutch ring 1201, with the preceding assembly, is fittedinto a step unit 1103 of the air supply sphere connector 101. The airsupply sphere 15 is screwed into the manifold 31 such that thetrapezoidal cutout units 1202 of the one-way clutch ring 1201 and thetrapezoidal protrusion units 1102 of the air supply sphere connector 101are fitted together. When the air supply sphere 15 approaches a state ofbeing tightly fitted into the manifold 31, the elastic ring 1203 of theone-way clutch ring 1201 makes contact with the interior surface of themanifold 31, and the resulting friction restrains the rotation of theelastic ring 1203. The air supply sphere 15 is screwed in, and a slantedportion 1103 of the trapezoidal protrusion units 1102 of the air supplysphere connector 101 overtops a slanted portion 1204 of the trapezoidalcutout units 1202 of the one-way clutch ring 1201, making a clickingsound. When the screwing of the air supply sphere 15 into the manifold31 is complete, the elastic ring 1203 is deformed, thus preventing theone-way clutch ring 1201 from spinning to no purpose, while alsosecuring the air supply sphere 15 firmly within the sphygmomanometermain body 1.

FIG. 13 depicts details of the display unit 11 of the sphygmomanometer1.

In FIG. 13, No. 110 is a systolic blood pressure display, No. 111 is adiastolic blood pressure display, No. 112 is a pulse rate display, No.113 is a pulse wave signal display, No. 114 is a previous value display,No. 115 is an exhaust display, No. 116 is an inadequate pressurizationdisplay, No. 117 is an excess pressurization display, and No. 118 is adisplay of which mode is currently being selected.

The systolic blood pressure display 110 displays pressure at anyinstance when both pressurizing and depressurizing, ultimatelydisplaying the systolic blood pressure. The diastolic blood pressuredisplay 111 displays the ultimately determined diastolic blood pressure.For example, if diastolic blood pressure is determined to be 80,operation wherein exhaust and depressurization at the same speed as thatused up to that point is pointless, and thus, the electromagnetic valve36 is controlled such that exhaust proceeds at high speed starting atpressure value 60. During high speed exhaust, the exhaust display 115flashes on and off. The exhaust display 115 flashes on and off even whenthe exhaust switch 14 is pressed. In such circumstance, theelectromagnetic valve is controlled to be forcibly released and exhaustat high speed. Exhaust speed during high speed exhaust is not less thandouble that during regular depressurization. The pulse rate display 112displays the measured pulse rate. The previous value display eitherflashes or lights steadily when the power switch 12 is pressed, anddisplays the systolic and diastolic blood pressure, as well as the pulserate, that were measured in the most recent measurement, on the systolicblood pressure display 110, the diastolic blood pressure display 111,and the pulse rate display 112, respectively. After a brief interval, orwhen air supply from the air supply sphere 15 commences, the displaylights go out, as does the flashing or steadily lit previous valuedisplay. A circumstance may also arise wherein the pressureinstantaneously increases during pressurization, i.e., instantaneouspressure increases, and if the raw instantaneous pressure data isdisplayed in the display unit, it is possible that a user may mistakenlyconclude that sufficient pressure is present. According to theembodiment, user confusion is avoided by having the display unit, i.e.,the systolic blood pressure display 110, display a blunted pressuredata, rather than displaying the instantaneous pressure data.

The pulse wave signal display 113 shows the size of the detected pulsewave signal, in a bar display. Whereas the bar will increase anddecrease rhythmically from left to right and back again for a personbeing measured who has a typical pulse, the bar will not moverhythmically for a person being measured who has an irregular pulse.Installing the pulse wave signal display 113 is thus highly useful, asit allows a visual determination of whether the person being measuredhas an irregular pulse or not.

When the inadequate pressurization display 116 is lit or is flashing, itmeans that pressure within the cuff 2 has not reached a level sufficientfor measurement, and motivates the user to use the air supply sphere tosupply air. When the excess pressurization display 117 is lit or isflashing, it means that pressure within the cuff 2 is at or above aprescribed pressure, for example, 320 mmHg or more, and motivates theuser to look thereat and stop the pressurization operation.

The display of which mode is currently being selected 118 shows whichmode has been selected using the mode switch 13. It displays which modeis selected, from among Normal, Slow, and Stethoscope. According to theembodiment, the display is made such that a black inverted triangle markthat is positioned above the mode display that is printed on the coverof the sphygmomanometer main body will either light or flash.

The mode selection allows changing speed of exhaust, ordepressurization. When Normal Mode is selected, exhaust speed isconfigured, for example, to 5±αmmHg/sec. Normal Mode has an advantage ofbeing comparatively shorter measurement time, as it has comparativelyfaster exhaust speed. On the other hand, pressure fluctuationmeasurement interval also increases, which, while posing no particularproblem when measuring a person with a stable pulse rate, it mayincrease measurement error when measuring blood pressure of a personwith an irregular pulse rate, as a pulse may be easily missed. Accordingto the embodiment, a Slow Mode is built in, and when Slow Mode isselected, the air supply rate is set to approximately half that ofNormal Mode, for example, 2.0-2.5 mmHg/sec. Slow Mode thus allowsviewing pressure change to be viewed in greater detail by depressurizingmore slowly than normal, allowing more accurate performance ofmeasurement of a person with an irregular pulse rate, who has a pulsethat may be easily missed. Stethoscope Mode uses a stethoscope formanual measurement, which is also configured to exhaust at approximatelyhalf the speed of Normal Mode, for example, 2.0-3.0 mmHg/sec.

According to the embodiment, a cuff size ranging from XS to XL isprovided, and it is important that exhaust speed not be affected by cuffsize. The opening and closing of the electromagnetic valve 38 iscontrolled, i.e., with feedback control, such that the bigger the cuffsize, the bigger the air capacity that is exhausted per second.

While not shown in the drawings, pressing the power switch 12 whilepressing the mode switch 13, and holding down the mode switch 13 for atleast one second, will change the display to the number of measurements.In such circumstance, the systolic blood pressure display 110 displaysthat the display is showing the number of measurements, and thediastolic blood pressure display 111 displays the number ofmeasurements, which may be made to display only in units of 100 or more,and to not display in units of 10 or less.

<Sphygmomanometer Control Circuit Block Diagram>

In FIG. 14, No. 91 is a control unit for controlling the circuitoverall, for example, a CPU, and No. 92 is a pressure sensor fordetecting the pressure of the cuff 2, both the large cuff 22 and thesmall cuff 23. No. 93 is a ROM that stores a control program and varioustypes of data, and No. 94 is a RAM that temporarily stores a computationresult or a measurement result. No. 95 is a drive unit for driving theelectromagnetic valve 38 in accordance with a control signal from thecontrol unit 91, and No. 96 is a buzzer that makes a prescribed warning.No. 97 is a battery power supply, and No. 98 is a power control unit forcontrolling the battery power supply.

First, the user presses the power switch 12, then uses the mode switch13 to select a mode. A display operation of the display unit 11 for thepressing of the power switch 12 and the mode selection are as previouslydescribed.

Air from the air supply sphere 15 passes through the manifold 31, and issent to the large cuff 22 via the manifold junction 32, the large cuffconduit 33, and the large cuff tube 18. A portion of the air from theair supply sphere is also supplied to the small cuff 23 via the bypasstube 34, the conduit junction 35, and the small cuff tube 19.

Air that branches off via the conduit junction 35 is supplied to thepressure sensor 92 via the pressure sensor conduit 36. During suchcircumstance, i.e., during pressurization, a pressure fluctuation valuedetected by the pressure sensor 92 is very large compared with apressure fluctuation value during measurement, i.e., depressurization.Consequently, if the detected pressurization fluctuation value meets orexceeds a prescribed value, the control unit 91 determines thatpressurization is currently underway, and outputs a control signal thatdirects the drive unit 95 to close the electromagnetic valve 38. Uponreceipt of the control signal, the drive unit 95 closes theelectromagnetic valve 38, keeping air from leaking out of theelectromagnetic valve 38. The air supply sphere 15 and the pressuresensor 92 are connected by the bypass tube 34, which is thinner than thelarge cuff conduit 33, which has the effect of blunting drasticpressurization. If the pressure increases drastically, there is a riskthat a large pressure value will be displayed in the display unit 11,and a user may mistakenly assume that sufficient pressure has beenachieved. Accordingly, it is possible to avoid such a mistakenassumption on the part of the user, by blunting a pressure change.

The buzzer 96 issues a sound in an instance that may include, but is notlimited to, when the power to the sphygmomanometer main body is switchedon and the display unit is activated, when the mode is changed via themode switch 13, when the blood pressure value is determined, or when anerror occurs.

The user views the value that is shown in the systolic pressure displayof the display unit 11, decides whether the pressurization in the largecuff 22 and the small cuff 23 is sufficient for measuring, and if thepressurization is determined to be sufficient, it stops air beingsupplied from the air supply sphere 15. In such circumstance, thepressure sensor 92 detects that the pressure fluctuation value, i.e.,the increase value, is effectively zero or in a depressurization state,within a prescribed time interval. The control unit 91 outputs a controlsignal that directs the drive unit 95 to open the electromagnetic valve38, and upon receipt of the control signal, the drive unit 95 opens theelectromagnetic valve 38 such that depressurization speed reaches aprescribed value. The operation of the sphygmomanometer switches frompressurization mode to measurement mode.

When in measurement mode, the systolic blood pressure and the diastolicblood pressure are measured according to a measurement program that isstored in the ROM 93. Determination operation of blood pressure value,etc., are described in detail with reference to the flowchart in FIG.17, and thus, only an overview will be presented for the present.

When air that is supplied to the large cuff 22 is gradually exhausted tothe outside according to depressurization, blood flow that has beenimpeded commences at a given point in time. The commencement of bloodflow gives rise to a fluctuation in pressure within the small cuff 23.The fluctuation in pressure is detected by the pressure sensor 92, andis treated as the point at which the building of a pulse wave signal isdetected. A successive pressure value vis-à-vis the detection of thepulse wave is stored sequentially as a measured value in the RAM 94. Thepressure value of the point at which the building of a pulse wave signalis detected or the successive pressure value that is stored sequentiallyare used in determining the systolic blood pressure and the diastolicblood pressure, as described hereinafter.

The pulse value is determined by detecting a number of pulses over aprescribed time interval, and converting to a number of pulses in a60-second period.

<Systolic Blood Pressure and Diastolic Blood Pressure DeterminationOperation>

In the flowchart in FIG. 17, the pressure value at time ofdepressurization, i.e., the DC waveform, is measured in step S101. Thepressure value at time of depressurization is shown in the graph in FIG.15. While there are locations within the graph wherein the pressurevalue changes drastically, they depict a change that occurs upon rapidexhaust following determination of the diastolic blood pressure valueand a passing of a prescribed time interval. The respective measuredpressure values are temporarily stored in the RAM 94. It is assumed thata time t=0 when supply of air is completed.

In step S102, an oscillation constituent, i.e., a fluctuation value, orAC constituent, that is contained within a pressure that is measured attime of depressurization, is extracted, and the extracted value isstored within the RAM 94. The oscillation constituent is extracted byfiltering the pressure value. A graph of the extracted oscillationconstituent is similar to that shown in FIG. 15.

In step S103, a first candidate point for a systolic blood pressurevalue, i.e., a first SYS, is obtained, in accordance with theoscillation property obtained in step S102. During a prescribed timeinterval from the commencement of depressurization, the oscillationconstituent is very slight, owing to blood being trapped, by the largecuff 21, in the arm of the person being measured. When blood flowrecommences according to reduction of pressure within the large cuff 21,there is a point of an initial dramatic build-up, i.e., the first SYS inFIG. 15. When a difference d1 between an actual measured amplitude valueand an estimated amplitude value of the point of build-up are within aprescribed range, for example, between 5% and 15%, of maximum pulse waveamplitude value, wherein actual measured amplitude value is greater thanestimated amplitude value, the blood pressure value, i.e., the DC value,corresponding to the point is treated as the first candidate point forthe systolic blood pressure value. The 15% is assumed because it ishighly possible, with a larger difference, that the value is abnormal.As depicted in FIG. 16, the estimated amplitude value is estimated froma temporally previous point, for example, the point that is three pointsprior to the present. “Candidate” in the present circumstance is by nomeans limited to the pressure value at the initial build-up pointsignifying the systolic blood pressure value, as there would be adisturbance in the pulse wave if, for example, the person whose bloodpressure is being measured has an irregular pulse. Accordingly,consideration is also given to a candidate value that is obtained with adifferent method, according to the embodiment.

In step S104, a second candidate point for a systolic blood pressurevalue, i.e., a second SYS, is obtained, in accordance with theoscillation property obtained in step S102. The second SYS is a point ofdramatic decline as seen from the maximum pulse wave amplitude value,and, as per FIG. 16, a difference d2 between an actual measuredamplitude value and an estimated amplitude value, wherein actualmeasured amplitude value is greater than estimated amplitude value, istaken to be a point that falls within 5 and 15% of the initial maximumpulse wave amplitude value, as seen from the maximum pulse waveamplitude value point. A blood pressure value, i.e., a DC value, whichcorresponds to the second SYS is treated as a second candidate for thesystolic blood pressure value.

In step S105, a third candidate point for the systolic blood pressurevalue, i.e., a statistical SYS, is obtained, which is a point that fallswithin a prescribed proportion of the maximum pulse wave amplitudevalue, and that forms a basis for experimental probability. Accordingly,the statistical SYS is valid when there is a plurality of build-uppoints, and it is unclear as to which is probable.

In step S106, if the difference between the first candidate for thesystolic blood pressure value, corresponding to the first SYS, and thesecond candidate for the systolic blood pressure value, corresponding tothe second SYS, is within a prescribed value, in mmHg, the processproceeds to step S107, wherein the first candidate for the systolicblood pressure value is determined to be the systolic blood pressurevalue.

If the difference falls outside a prescribed range, the process proceedsto step S108, wherein, for example, the average of the first throughthird candidates for the systolic blood pressure value is determined tobe the systolic blood pressure value. It is permissible to applyweighting to the three values as well.

In step S109, diastolic blood pressure value is computed. As is clearfrom FIG. 15, while the envelope becomes progressively smaller from themaximum pulse wave amplitude value, the point where it reaches theprescribed proportion of the maximum pulse wave amplitude value is takenas the point that depicts the diastolic blood pressure value, i.e., theDIA, and the blood pressure value, i.e., the DC value, is determined tobe the diastolic blood pressure value. It is not absolutely necessary toexecute computation of the determination of the diastolic blood pressurevalue after determination of the systolic blood pressure value; rather,it may executed prior, or in parallel, thereto as well.

The systolic and diastolic blood pressure values thus derived aredisplayed in the display unit 11.

Whereas, in the present circumstance, if the difference between thefirst candidate for the systolic blood pressure value and the secondcandidate for the systolic blood pressure value falls outside theprescribed range, the average of the first through third candidates forthe systolic blood pressure value is taken to be the systolic bloodpressure value, it is also permissible for the average of the first andthird candidate values, or the third candidate value, to be taken to bethe systolic blood pressure value. It is also permissible for theaverage of the first and third candidate values to be taken to be thesystolic blood pressure value, regardless of whether or not thedifference between the first candidate for the systolic blood pressurevalue and the second candidate for the systolic blood pressure valuefalls within the prescribed range. It is further permissible to derivethe first and second candidate values, and take the average thereof tobe the systolic blood pressure value.

Whereas, according to the embodiment, unless otherwise specified, aplurality of build-up points are detected and a systolic blood pressurevalue ultimately derived as a systolic blood pressure value candidate,it is also permissible to use the algorithm depicted in the flowchart inFIG. 17 to determine the systolic blood pressure value and the diastolicblood pressure value, instead. While the property of pressurefluctuation at time of depressurization is as per FIG. 15, the systolicblood pressure value is obtained by the same algorithm, as depicted inFIGS. 23A and 23B, deriving the property of pressure fluctuation at timeof pressurization, i.e., increasing pressure, and detecting a pluralityof systolic blood pressure value candidates, i.e., the first SYS, thesecond SYS, etc., as per the figures.

<Assembly and Operation of the Electromagnetic Valve 38>

FIG. 18 depicts an assembly of the electromagnetic valve 38 that is usedaccording to the embodiment. In FIG. 18, No. 381 depicts a rubber valve,No. 382 a first plunger, No. 383 a plunger receptacle, No. 384 a spacer,and No. 385 a second plunger, respectively.

The rubber valve 381 protrudes from the first plunger only to the extentof a space S. The rubber valve 381 prevents air from leaking from theelectromagnetic valve 38, during pressurization, for example, by sealinga channel of the plunger receptacle 383. The rubber valve 381facilitates exhaust, during depressurization, for example, bywithdrawing from the plunger receptacle 383 and releasing the channel.The plunger receptacle 383 and the first and second plungers 382 and 385are formed of a conductive metal. A voltage is applied to both ends ofthe electromagnetic valve 38, an electromagnetic force acts between themetallic plunger 382 and the plunger receptacle 383, and the greater theimpressed voltage, for example, from 1.2 volts to a maximum of 1.7 or1.8 volts, the greater the size of the electromagnetic force.

FIG. 19 is a graph that depicts a hysteresis property when an openingand closing operation of the electromagnetic valve 38 is performed undernormal circumstances. In the graph in FIG. 19, the horizontal axisdepicts the voltage being impressed upon the electromagnetic valve 38,when PWM control is being performed, and expressed as a percentage, andthe vertical axis depicts the valve release stroke, with zero signifyingthe valve being fully opened. In FIG. 19, a curve L1 depicts thehysteresis when closing the electromagnetic valve 38, and a curve L2depicts the hysteresis when opening the selfsame valve.

When a voltage is gradually impressed, beginning when theelectromagnetic valve 38 is fully opened, as per the curve L1, theelectromagnetic valve 38 gradually begins to close at a point where thePWM reaches approximately 40%. When a point P1 is reached, wherein thePWM approaches approximately 50%, the channel is closed by the rubbervalve 381, i.e., the release stroke approaches approximately −195 μm. Atsuch point in time, the rubber valve 381 is still in a state of notbeing completely closed, and air is escaping. If further voltage isimpressed, the channel is completely sealed by the flexible rubber valvebeing deformed. The stroke at the point in time of complete seal, i.e.,a point P2, is approximately −340 μm.

When releasing the electromagnetic valve 38, i.e., curve L2, from thecompletely sealed state, i.e., P2, the impressed voltage is graduallylowered. The deformed rubber valve 381 returns to its original shapeaccording to the fall in impressed voltage, and air escapes through agap between the rubber valve 381 and the plunger receptacle 383, as therubber valve 381 penetrates a right-hand edge of a control region E1.The electromagnetic valve 38 is in a semi-open state, and when theimpressed voltage, i.e., the PWM, drops, the volume of air escapingthrough the gap increases commensurately. The electromagnetic valve 38is fully open at a point P3, wherein the PWM is approximately 44%, andthe release stroke is approximately −200 μm. Depressurization speed iscontrolled to be 5 mmHG/second according to the embodiment, and thecontrol is executed within the control region as per FIG. 19.

In the present circumstance, the control region is a region bounded byE1 and E2, and is the region wherein exhaust is controlled with adepressurization speed of 5 mmHg/second. Voltage that corresponds to thecontrol region is taken to be electromagnetic valve control voltage,i.e., between approximately 0.6 and approximately 1.0 volts, or betweenapproximately 50% and approximately 64% PWM, for example, according tothe embodiment. Whereas depressurization speed does not immediatelyreach 5 mmHg/second at the point in time of penetrating into the controlregion, i.e., PWM=E1, it is the point in time at which control commencesin the direction of the given depressurization speed, and at whichexhaust commences. Whereas the rubber valve 381 opens as impressedvoltage drops, impressed voltage is controlled so as to achieve andmaintain a depressurization speed of 5 mmHg/second. As depressurizationproceeds, pressure within the cuff 2 drops, and the degree of opening ofthe rubber valve increases as well. When a left-hand edge of the controlregion, i.e., PWM=E2, is reached, control to maintain a depressurizationspeed of 5 mmHg/second ends, and rapid exhaust is executed. At suchtime, the cuff 2 pressure is configured to 20-30 mmHg, for example.

Force that maintains the closure state of the electromagnetic valve 38between the points P1 and P2, and the points P2 and P3, iselectromagnetic force from impressed voltage between the first plunger382 and the plunger receptacle 383. Accordingly, a change in the releasestroke between the points P2 and P3 is mild, whereas a change in therelease stroke is more dramatic after release, i.e., after the point P3,as there is no more effect from electromagnetic force.

According to the embodiment, an electromagnetic valve is used whoseopening and closing operation is controlled by impressed voltage, andthus, it is possible to close the electromagnetic valve 38 rapidly whensending air from the air supply sphere 15, i.e., during pressurization,and it is also possible to exhaust air within the cuff 2 in a stablemanner when exhausting, i.e., during depressurization, as per theforegoing mode.

In order to perform the opening and closing operation in a stablemanner, however, it becomes important to achieve a movement in thedirection of the Y-axis, while the rubber valve 381 and the firstplunger 382 are maintained in a horizontal orientation, as depicted inFIG. 18. Accordingly, when the electromagnetic valve 38 tilts, which mayeasily occur, as depicted in FIG. 20, a negative effect occurs in thatthe first plunger 382 and the plunger receptacle 383 will make contact,the electromagnetic force between the two metals will bond the twometals together, and the electromagnetic valve 38 will not be releasedeven if a voltage is impressed, i.e., at point P3, that would otherwiserelease the electromagnetic valve 38.

FIG. 21 depicts a hysteresis property when the electromagnetic valve 38is closed in such a tilt state.

When a voltage is gradually impressed from the fully open state of theelectromagnetic valve 38, as per a curve L3, the electromagnetic valve38 begins to close at the point when the PWM reaches approximately 40%.When a point P4, i.e., when the PWM approaches approximately 55%, thechannel is closed by the rubber valve 381, which is tilted at a slant,as per FIG. 20, i.e., the release stroke approaches approximately −230μm. Whereas the channel is nearly completely sealed by the deformedelastic rubber valve if further voltage is impressed, the first plunger382 and the plunger receptacle 383 will make contact at a point P5,which occurs prior to reaching the state of complete seal, i.e., thepoint P2, and the two will be drawn together by the electromagneticforce arising from the impressed voltage. The first plunger 382 and theplunger receptacle 383 will thus reach the point P2, the state of seal,in the state of being drawn together. In such circumstance, the strokeis approximately −340 μm, similar to FIG. 19.

When releasing the electromagnetic valve 38 from the state of completeseal, i.e., the point P2, as per the curve L4, the impressed voltage isgradually lowered. The deformed rubber valve 381 returns to its originalshape according to the fall in impressed voltage, and even in such astate, the first plunger 382 and the plunger receptacle 383 willcontinue to adhere together because of the electromagnetic force, andthe metal contact is released at a point P6, wherein the PWM isapproximately 48%, and the release stroke is approximately −300 μm. Evenif the voltage enters the control region, there is almost no change inthe stroke of the rubber valve 381, before a point P6 is reached, owingto the effect of the adhesion from the electromagnetic force. When thepoint P6 is passed, the adhesion between the first plunger 382 and theplunger receptacle 383 is broken, and the rubber valve 381 opensdramatically. Consequently, there is a dramatic change in the hysteresisL4. When the point P6 is passed, the electromagnetic valve 38 is in asemi-open state, and air begins to escape through the gap. A furtherfall in the impressed voltage will completely open the electromagneticvalve 38 at a point P7, wherein the PWM is approximately 43%, and thestroke is approximately −220 μm.

The force that maintains the electromagnetic valve 38 in a closed statebetween the points P4-P5-P2, and between the points P2-P6, is theelectromagnetic force between the first plunger 382 and the plungerreceptacle 383 as a result of the impressed voltage, similar to thesituation in FIG. 19. Accordingly, the change in stroke between thepoints P2-P6 is mild. Conversely, after the metal contact is released,i.e., after the point P6, the impressed voltage at the point in time inquestion, i.e., the PWM, should gradually release the rubber valve 381,thus giving rise to a dramatic stroke change, wherein the rubber valve381 is completely released at the point P7.

When the metal adhesion occurs, the rubber valve 381 begins to opendramatically, i.e., P6, and it becomes difficult to maintain thedepressurization speed of approximately 5 mmHg/second. In fact, asdepicted in FIG. 21, it is clear that there is no change in the strokeof the rubber valve 381 from the point that the control region isentered until the point P6, and almost no air is escaping.

Whereas the difference in the PWM that opens the rubber valve 381 andthe PWM that closes the rubber valve 381 when the electromagnetic valve38 is operating opening and closing normally, with no metal adhesionoccurring, is approximately 6%, the difference in the PWM when metaladhesion has occurred is approximately 12%. The problem is that whensuch metal adhesion is present, dramatic valve opening and closingoperation of the foregoing sort occurs, which interferes with stableexhaust, i.e., depressurization, of the cuff 2. While the problem issolved if the electromagnetic valve 38 can be inserted and removedhorizontally at all times, the control thereof is challenging in theextreme.

According to an improvement of the embodiment, a component 386, of thefirst plunger 382 of the electromagnetic valve 38, that has potential tomake contact, is cut so as to taper almost completely in the orientationof the circumference. Making the component 386, that has potential tomake contact with the plunger receptacle 383, by tilting the firstplunger 382, taper in such fashion, allows maintaining a degree of spacebetween the first plunger 382 and the plunger receptacle 383, thusavoiding metal contact even if the electromagnetic valve 38 should tiltto some extent. Configuring an angle φ of the taper cut component, i.e.,No. 386, to be between approximately five degrees and approximatelyeight degrees, is highly efficacious, as it allows keeping an effect ofslanting under control, as well as keeping the electromagnetic forcebetween the first plunger 382 and the plunger receptacle 383 frombecoming excessively weak. The angle φ is not limited thereto, however,and tapering to a varying degree will be effective to some extentagainst slanting.

Tapering the first plunger 382 causes the hysteresis to have theproperty shown in FIG. 19, even if the rubber valve 381 is slanted,facilitating stable execution of depressurization speed control.

The present invention is not limited to the embodiments describedherein. A variety of alterations and transformations are possiblewithout deviating from the spirit or the scope of the present invention.Accordingly, the claims are attached hereinafter in order to publish thescope of the present invention.

1. A sphygmomanometer comprising: a cuff; a pressure sensor measuring apressure of the cuff; a memory storing pressure values measured by thepressure sensor during depressurization of the cuff; a control unitdetermining a systolic blood pressure based on the pressure valuesstored in the memory; wherein the control unit obtains a pressure valueas a first candidate from the stored pressure values at a point where anamplitude of the pressure dramatically increases a first time; thecontrol unit obtains a pressure value as a second candidate from thestored pressure values at a point where the amplitude of the pressuredramatically decreases the first time as seen from a point of a maximumamplitude of the pressure; and the control unit determines a bloodpressure corresponding to the first candidate as the systolic bloodpressure when the difference between the first candidate and the secondcandidate is within a prescribed value.
 2. The sphygmomanometeraccording to claim 1, wherein the control unit determines, as adiastolic blood pressure, a blood pressure corresponding to the pressurevalue which reaches a prescribed proportion of the maximum amplitude thefirst time after the maximum amplitude.
 3. The sphygmomanometeraccording to claim 1, wherein the control unit obtains a pressure valuewhich falls within a prescribed proportion of the maximum amplitude as athird candidate from the stored pressure, and the control unitdetermines a blood pressure corresponding to an average value of thefirst, second and third candidates as the systolic blood pressure whenthe difference between the first candidate and the second candidate isnot within the prescribed value.
 4. A sphygmomanometer comprising: acuff; a pressure sensor measuring a pressure of the cuff; a memorystoring pressure values measured by the pressure sensor duringdepressurization of the cuff; a control unit determining a systolicblood pressure based on the pressure values stored in the memory;wherein the control unit obtains a pressure value as a first candidatefrom the stored pressure values at a point where a difference between asquared value of a measured amplitude of the pressure and a squaredvalue of an estimated amplitude of the pressure is within a firstprescribed percentage range of a maximum amplitude of the pressure for afirst time, the estimated amplitude being estimated from temporallyprevious pressure values; the control unit obtains a pressure value as asecond candidate from the stored pressure values at a point where adifference between the squared value of the measured amplitude of thepressure and the squared value of the estimated amplitude of thepressure is within a second prescribed percentage range of the maximumamplitude for the first time as seen from a timing of the maximumamplitude; and the control unit determines a blood pressurecorresponding to the first candidate as the systolic blood pressure whenthe difference between the first candidate and the second candidate iswithin a prescribed value.
 5. The sphygmomanometer according to claim 4,wherein the control unit determines, as a diastolic blood pressure, ablood pressure corresponding to the pressure value which reaches aprescribed proportion of the maximum amplitude the first time after themaximum amplitude.
 6. The sphygmomanometer according to claim 4, whereinthe control unit obtains a pressure value which falls within aprescribed proportion of the maximum amplitude as a third candidate fromthe stored pressure, and the control unit determines a blood pressurecorresponding to an average value of the first to third candidate as thesystolic blood pressure when the difference between the first candidateand the second candidate is not within the prescribed value.